1. Field of the Invention
The present invention relates to a packaging container and a method for manufacturing the same. More particularly, the present invention relates to a packaging container capable of heating or warming the contents thereof and a method for manufacturing the same.
2. Description of the Related Art
Packaging containers made of a tightly sealable resin film are often used as a container for packaging foods, a container for storing various small articles, and the like. These packaging containers have a high air-tight property and are hygienic due to sterilization by being pressurized and heated, so that the contents in the container can be preserved for a long period of time. Moreover, at using, the contents can be warmed by immersion into hot water, use of a microwave oven, or the like in a state in which the contents are stored in the packaging container. In the case in which the contents are constituted of foods, cooking of the foods can also be carried out easily.
Typically, such a packaging container may be one in which a laminate film having a resin such as vinylidene chloride excellent in shielding against oxygen interposed therein, for example, is thermally fused to an opening part of an upper plane of the container body that stores the contents, so as to enclose the contents (for example, see Japanese Patent Application Laid-Open (JP-A) No. 2000-34448). In this case, when a packaging container having such a tightness property is warmed, the packaging container may be exploded to let the contents fly out, so that the packaging containers are perforated at several sites thereof in advance by using a fork or the like before warming. Also, the warming is often carried out several times. A process is often carried out in which, after the top seal (easily openable sealed part) of the packaging container is peeled off and the contents are stirred, the packaging container is covered with a cover film and warmed, and thereafter the contents in the packaging container are stirred and warmed again. In this case, it requires a cumbersome work of perforating the packaging container and further a stirring work, and moreover, the contents may fly out from the holes depending on the way of forming the holes, so that it has not been preferable.
Also, in order that the perforating work may not be needed, a packaging container is used in which the contents are warmed after the seal of the container is partly peeled off before warming. This packaging container is subjected to an easy-opening treatment in advance so that a specific site of the seal may be easily peeled off. Such an easy-opening treatment may be a method in which a slit is formed in advance at one end of the laminate film thermally fused to the container body, and the container is tightly closed with a special ink serving also as an adhesive agent. However, this method may be disadvantageous in that, when the contents stored in the container body are liquid substances or gas-substituted packaged substances, the contents may leak out from the slit during the transportation to consumer markets. Moreover, because the easy-opening treatment is required, there is a problem of rise in the production costs of the container itself.
Therefore, an object of the present invention is to provide, with a simple construction, a packaging container by which leakage can be prevented with certainty even when the contents stored in the packaging container are liquid substances or gas-substituted packaged substances, and moreover, breakage of the packaging container and flying-out of the contents accompanying the pressure rise in the inside of the container accompanying the warming can be prevented in warming the contents together with the container body, as well as a method for manufacturing the same.